The present invention relates to a new and improved construction of a sample preparation device for an analytical laboratory.
Before an analysis operation can be carried out on a sample, the sample must be put into a form which is suitable for the method of analysis to be used, for example a solution. However, the starting substance available is frequently a solid substance, which must therefore be crushed and dissolved or extracted. Heretofore the crushing operation was often carried out by means of a mortar and pestle or by means of a ball mill, the crushed sample then being dissolved or extracted, and finally the remaining residue being separated off by filtering. Some devices have been proposed which operate with ultrasonic or mechanical grinding mechanism to which the solvent is added so that the dissolving or extracting operation is carried out during the crushing operation. The resulting suspension is then, typically, taken from the crushing mechanism and fed to a filter or a centrifuge, by means of suitable intermediate containers for carrying the sample from the crushing mechanism to the filter or centrifuge.
A typical mode of operation as briefly set out above suffers from a number of fundamental weaknesses. The fact that the sample must be taken backwards and forwards by means of intermediate containers, possibly a number of times, between the individual devices (for example the mill and the filter device) involves a relatively expensive, tedious and complicated procedure. In addition the danger of contamination of the sample when transferring it from one device to the other is great, for example residues of one sample can be carried over into another sample, unless extreme care is taken, and this in turn has a direct effect on the time required for and the cost of the analysis operation. In addition, the number of times that a sample is transferred influences the degree of precision of analysis, due to losses of the original substance.